You aren't getting it.
BUYERS (in this case, YOU) can leave the seller any feedback.
SELLERS can't leave a buyer anything but a positive. Which sucks because if you have a deadbeat buyer, well, too bad, you can't do anything about it. I suppose you could just not leave anything, but that's not as good as leaving a negative to warn others.
Part of me sees why this happened. I got a retaliatory feedback once for no good reason. It was only a neutral (I left him a neutral due to really bad packaging) but still it was really dumb. However, now buyers in general know they can get away with stuff and can't get a negative over it.
I'll still buy on ebay, but I won't sell. Never did because of the fees and stupid people, but now I have even less of a reason to sell. A buyer's feedback on ebay means almost nothing now.